The use of porous abrasives tools to improve mechanical grinding processes is generally well known. Pores of an abrasive tool typically provide access to grinding fluids, such as coolants and lubricants, which tend to promote more efficient cutting, minimize metallurgical damage (e.g., surface burn), and maximize tool life. Pores also permit the clearance of material (e.g., chips or swarf) removed from the workpiece being ground, which is important especially when the workpiece being ground is relatively soft or when surface finish requirements are demanding (e.g., such as the case when back-grinding silicon carbide wafers).
Techniques for fabricating abrasive tools having porosity may generally be classified into one of two categories. In the first category, a pore structure is created by the addition of organic pore inducing media, such as ground walnut shells or plastic beads of the appropriate dimensions, into the abrasive article. These media are sacrificial, in that they thermally decompose upon firing, leaving voids or ‘pores’ in the cured abrasive tool. Examples of this category are discussed in U.S. Pat. Nos. 5,221,294 and 5,429,648. In the second category, a pore structure may be created by the addition of closed cell materials, such as bubble alumina, into an abrasive article. Unlike sacrificial media, this type of media survives the firing process, and remains in the cured abrasive tool to form pores. Examples of this category are discussed, for example, U.S. Pat. No. 5,203,886. Each of U.S. Pat. Nos. 5,221,294, 5,429,648, and 5,203,886 is herein incorporated by reference in its entirety.
In an alternative approach, porosity can be achieved within an abrasive article through the use of fiber-like abrasive grains having a length to diameter aspect ratio of, for example, 5:1 or greater. Examples of this approach are discussed in U.S. Pat. Nos. 5,738,696 and 5,738,697, each of which is herein incorporated by reference in its entirety. The poor packing characteristics of the elongated abrasive grains result in an abrasive article including increased porosity and permeability and suitable for relatively high-performance grinding. In another alternative approach, porosity can be created within an abrasive article by the leaching of a filler, such as common salt. Examples of this approach are discussed in U.S. Pat. Nos. 6,685,755 and 6,755,729, each of which is herein incorporated by reference in its entirety.
As market demand has grown for precision components in products such as engines, refractory equipment, and electronic devices (e.g., silicon and silicon carbide wafers, magnetic heads, and display windows), the need has grown for improved abrasive tools for fine precision grinding and polishing of ceramics and other relatively hard and/or brittle materials. Therefore, there exists a need for improved abrasive articles and abrasive tools, and in particular, those including a relatively high degree of porosity.